Kamiya Y.,Nagoya University |
Kamiya Y.,EcoTopia Science Institute |
Asanuma H.,Nagoya University
Accounts of Chemical Research | Year: 2014
ConspectusDNA is regarded as an excellent nanomaterial due to its supramolecular property of duplex formation through A-T and G-C complementary pairs. By simply designing sequences, we can create any desired 2D or 3D nanoarchitecture with DNA. Based on these nanoarchitectures, motional DNA-based nanomachines have also been developed. Most of the nanomachines require molecular fuels to drive them. Typically, a toehold exchange reaction is applied with a complementary DNA strand as a fuel. However, repetitive operation of the machines accumulates waste DNA duplexes in the solution that gradually deteriorate the motional efficiency. Hence, we are facing an "environmental problem" even in the nanoworld. One of the direct solutions to this problem is to use clean energy, such as light. Since light does not contaminate the reaction system, a DNA nanomachine run by a photon engine can overcome the drawback of waste that is a problem with molecular-fueled engines.There are several photoresponsive molecules that convert light energy to mechanical motion through the change of geometry of the molecules; these include spiropyran, diarylethene, stilbene, and azobenzene. Although each molecule has both advantages and drawbacks, azobenzene derivatives are widely used as "molecular photon engines". In this Account, we review light-driven DNA nanomachines mainly focusing on the photoresponsive DNAs that we have developed for the past decade. The basis of our method is installation of an azobenzene into a DNA sequence through a d-threoninol scaffold. Reversible hybridization of the DNA duplex, triggered by trans-cis isomerization of azobenzene in the DNA sequences by irradiation with light, induces mechanical motion of the DNA nanomachine. Moreover we have successfully developed azobenzene derivatives that improve its photoisomerizaition properties. Use of these derivatives and techniques have allowed us to design various DNA machines that demonstrate sophisticated motion in response to lights of different wavelengths without a drop in photoregulatory efficiency.In this Account, we emphasize the advantages of our methods including (1) ease of preparation, (2) comprehensive sequence design of azobenzene-tethered DNA, (3) efficient photoisomerization, and (4) reversible photocontrol of hybridization by irradiation with appropriate wavelengths of light. We believe that photon-fueled DNA nanomachines driven by azobenzene-derivative molecular photon-fueled engines will be soon science rather than "science fiction". © 2014 American Chemical Society.
Sakakura A.,EcoTopia Science Institute |
Ishihara K.,Nagoya University
Chemical Society Reviews | Year: 2011
The rational design of small but highly functional artificial catalysts is very important for practical organic synthesis. Asymmetric Lewis acid catalyses with non-covalent secondary interactions have been developed for enantioselective reactions. This tutorial review describes the concept, design and examples of asymmetric Cu(ii) catalyses for cycloaddition reactions based on intramolecular π-cation or n-cation interactions between the copper(ii) cation and auxiliary Lewis basic sites of the chiral ligands. © 2011 The Royal Society of Chemistry.
Yuzawa H.,Nagoya University |
Yoshida T.,EcoTopia Science Institute |
Yoshida H.,Nagoya University
Applied Catalysis B: Environmental | Year: 2012
Photocatalytic hydrogen production from aqueous ethanol was investigated over Au-loaded titanium oxide under visible light (510-740. nm) irradiation. Hydrogen was constantly produced through the present plasmonic photocatalysis. In this system, Au nanoparticles with larger particle size were essentially effective for the reaction due to the high efficiency for the localized surface plasmon resonance (LSPR). Further, Au nanoparticles with short rod-like shapes were more effective for the reaction than those with spherical shape because of the higher efficiency for the electron transfer from the Au nanoparticle to the conduction band of titanium oxide. On the other hand, aggregates of the Au nanoparticles were not appropriate for the reaction, which derived from the low efficiency of the electron transfer. Finally, titanium oxide containing anatase phase with larger particle size was most preferred for the reaction. © 2011 Elsevier B.V..
Uchiyama T.,EcoTopia Science Institute
Powder Technology | Year: 2013
This study proposes a simulation method for incompressible gas flow laden with small solid particles. It is based on a Vortex in Cell (VIC) method, which was originally developed to simulate incompressible single-phase flows. The proposed VIC method discretizes the gas vorticity field into vortex elements and computes the time evolution of the two-phase flow by calculating the behavior of the vortex element as well as the particle motion with the Lagrangian approach. This study also applies the VIC method to simulate a free fall of small solid particles in an unbounded air. The particles, initially arranged within a spherical region in a quiescent air, are made to fall, and their fall induces the air flow around them. The interactions between the particle motion and the air flow are favorably compared with the existing measured and simulated results, demonstrating the validity of the proposed VIC method. © 2012 Elsevier B.V.
Bratescu M.A.,EcoTopia Science Institute |
Saito N.,Nagoya University
Journal of Physical Chemistry C | Year: 2013
We present a facile, one-step, and surfactant-free method for direct synthesis and loading of stable gold and gold-alloy nanoparticles (NPs) on large-area graphene using an electrical discharge in a liquid environment, termed solution plasma. We observed a charge doping of graphene by the gold NPs, which depends on the particles' chemical composition, even if the NPs contain a few percent of trivalent sp metals, such as indium (In) or gallium (Ga). Raman and electron energy loss spectroscopy (EELS) methods show that graphene is doped with electrons (n-type) in the case of gold NPs and with holes (p-type) in the case of gold-alloy NPs. The Raman band shift indicates that the amount of the transferred electrons from the gold NPs to graphene is -2 × 10 -4 electrons per unit cell. The gold-alloy NPs receive from graphene (2 and 4) × 10-5 electrons per unit cell if the gold NPs contain In and Ga, respectively. In the EELS spectra, the decrease in the intensity of the 1s-π* transition and the shift of the π* peak to higher energy confirm the depopulation of the antibonding states caused by the electron transfer from graphene to the gold-alloy NPs. © 2013 American Chemical Society.